This invention relates to engine valve trains and, more particularly, to a two-step valve train using direct acting switching valve lifters with dual intake valves and cams combined for varying modes of operation.
The current state of engine valve trains or valve actuating mechanisms abounds with devices for changing the timing and/or lift of engine valves, particularly intake valves, during operation of the engine in order to improve engine fuel efficiency, reduce exhaust emissions and increase performance.
Among the recently reported arrangements is one in which overhead camshafts actuate rocker arms that operate the intake and exhaust valves of the engine. The camshafts include multiple cams that operate through alternate rocker arm actuators to selectively provide high lift or low lift levels of intake and exhaust valve operation. A camshaft phase changer may be included which varies the phase of the intake valves to desirably alter the valve timing for different operating modes.
Another system utilizes direct acting switching valve lifters driven by an overhead camshaft. The camshafts have high lift and reduced lift cams to allow changing of the valve lift from a high lift mode to a low lift mode. The low lift cams for the two intake valves are identical so that all the valves operate with identical high lift profiles which are selectively replaceable by operation on identical low lift profiles. Again, a camshaft phase adjuster may be provided to alter the relative camshaft positions for varying the phase of the intake and exhaust camshafts.
In a third known arrangement, so-called switching lifters have been proposed for deactivating, or cutting out, operation of some of the cylinders of an engine by switching the valves to a no lift mode. Then engine operation is continued entirely by the remaining operational cylinders. Currently-available forms of switching or displacement on demand valve lifters may be utilized for this type of operation.
The present invention provides an improved valve train which utilizes variations of current technology together with innovative combinations thereof to provide various operational alternatives not found in the known prior art.
In one form of the invention, modifications of known direct acting valve lifters are utilized to provide high lift or low lift intake valve actuation as well as comparable exhaust valve actuation, utilizing the modified two-step valve lifters for direct actuation of the valves, as compared to indirect actuation through rocker arms or other mechanisms. Single or dual cam phasers may be added to the combination if desired for varying valve timing events.
The arrangement provides a compact valve train avoiding the extra mechanisms involved with additional intermediate components, such as rocker arms or push rods in a valve train system. Additionally, the low lift cams for the dual intake valves for each cylinder are ground to provide variations in the valve lift, and also timing if desired, in order to provide improved swirl and mixing of the cylinder charge during low speed operation of the engine.
In an alternative embodiment, a group of, preferably half of, the engine cylinders may be arranged for reduced valve lift operation at a zero lift FIGURE. This shuts off both intake and exhaust valves on these cylinders while continuing to operate the engine on the remaining cylinders for more efficient low speed and load engine operation.
The operating cylinders may be programmed to be operated either in the high lift or low lift modes of operation, depending on the engine requirements for operation of the associated vehicle, in order to provide the most efficient operating conditions. When fast acceleration or high speed operation are required, both groups of cylinders are switched back to high lift operation to provide for full engine output if required. When operated in the low lift mode, the intake valves are again operated with differing lifts so that a primary intake valve is open a greater amount to provide advantageous cylinder swirl and charge mixing conditions and the secondary valve is opened sufficiently to add slightly to the cylinder charge while maintaining the ports in operating condition for immediate return to high lift operating mode as required.
With any of these alternatives, one or two can phasing devices may be mounted on the single or dual camshafts to provide variations in cam timing as may be desirable for the various operating modes.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.